In a conventional method of manufacturing a glass panel as noted above, a paste-like thermally meltable seal member is applied between the glass plates at the entire peripheries thereof, heated to 480° C. or above, for example, to be melted, and then cooled to room temperature to be hardened, thereby to execute a heat-joining process for joining both the glass plates throughout the circumference thereof to be hermetically sealed. After the heat-joining process is completed, that is, after the thermally meltable seal member is cooled to room temperature and hardened, a decompression process is executed to decompress the void between the glass plates.
However, since the void between the glass plates is decompressed after the thermally meltable seal member becomes hard, an internal stress is produced in the glass plates by atmospheric pressure acting on the glass surfaces. Specifically, an excessively long outer edge dimension between outermost rows of the space-maintaining members positioned closest to edges of the glass plates and the thermally meltable seal member could result in a great internal stress to damage the glass plates easily.
Under the circumstances, Applicant has conducted various experiments based on a finding that the internal stress produced in the glass plates is related to the thickness of the glass plates and the outer edge dimension noted above. As a result, it has been found that the outer edge dimension should be set not to exceed 13.2 times the thickness of the thinner of the glass plates in order to keep the internal stress produced in the glass plates within a long-term permissible strength (100 kgf/cm2). A patent application describing this finding has been filed (see Patent Unexamined Publication No. 11-324509).
As in the prior art, the technique disclosed in the above-noted publication is also based on that the thermally meltable seal member is cooled and hardened after the heat-joining process is executed and then the decompression process is executed. Thus, the problem set forth below remains to be solved.
Having being heated to 480° C. or above in the heat-joining process, the glass plates generate inorganic substances containing Na while the thermally meltable seal member generates organic substances from a binder mixed in the seal member. These inorganic and organic substances could adhere to inner surfaces of the glass plates as a result of the cooling process, thereby to lower the quality of the glass panel due to a deterioration in permeability or the like. There is room for improvement in this respect.
The present invention has been made having regard to the conventional problem noted above, and its object is to provide a method of manufacturing a glass panel and a glass panel manufactured by such a method, in which the inorganic and organic substances generated in time of the heat-joining process are prevented from adhering to the inner surfaces of the glass plates as much as possible and yet the internal stress produced in the glass plates can be kept to a desired value or less.